SERVER-27745: Implement LogicalClock

1 files changed, 100 insertions, 0 deletions

diff --git a/src/mongo/db/logical_clock.h b/src/mongo/db/logical_clock.h
new file mode 100644
index 00000000000..3119b75f225
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+++ b/src/mongo/db/logical_clock.h
@@ -0,0 +1,100 @@
+/**
+ *    Copyright (C) 2017 MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/signed_logical_time.h"
+#include "mongo/stdx/mutex.h"
+
+namespace mongo {
+class TimeProofService;
+class ServiceContext;
+class OperationContext;
+
+/**
+ * LogicalClock maintain the clusterTime for a clusterNode. Every cluster node in a replica set has
+ * an instance of the LogicalClock installed as a ServiceContext decoration. LogicalClock owns the
+ * TimeProofService that allows it to generate proofs to sign LogicalTime values and to validate the
+ * proofs of SignedLogicalTime values.LogicalClock instance must be created before the instance
+ * starts up.
+ */
+class LogicalClock {
+public:
+    // Decorate ServiceContext with LogicalClock instance.
+    static LogicalClock* get(ServiceContext* service);
+    static LogicalClock* get(OperationContext* ctx);
+    static void set(ServiceContext* service, std::unique_ptr<LogicalClock> logicalClock);
+
+    /**
+     *  Creates an instance of LogicalClock. The TimeProofService must already be fully initialized.
+     *  The validateProof indicates if the advanceClusterTime validates newTime. It should do so
+     *  only when LogicalClock installed on mongos and the auth is off.
+     */
+    LogicalClock(ServiceContext*, std::unique_ptr<TimeProofService>, bool validateProof);
+
+    /**
+     * The method sets clusterTime to the newTime if the newTime > _clusterTime and the newTime
+     * passes the rate check and proof validation.
+     * Returns an error if the newTime does not pass the rate check or proof validation,
+     * OK otherwise.
+     */
+    Status advanceClusterTime(const SignedLogicalTime& newTime);
+
+    /**
+     * Returns the current clusterTime.
+     */
+    SignedLogicalTime getClusterTime();
+
+    /**
+     * Returns the next  clusterTime value and provides the guarantee that the next reserveTicks
+     * call will return the value at least nTicks ticks in the future from the current clusterTime.
+     */
+    LogicalTime reserveTicks(uint64_t nTicks = 1);
+
+    /**
+     * Resets _clusterTime to the signed time created from newTime. Should be used at the
+     * initialization after reading the oplog. Must not be called on already initialized clock.
+     */
+    void initClusterTimeFromTrustedSource(LogicalTime newTime);
+
+private:
+    /**
+     * Utility to create valid SignedLogicalTime from LogicalTime.
+     */
+    SignedLogicalTime _makeSignedLogicalTime(LogicalTime);
+
+    ServiceContext* _serviceContext;
+    std::unique_ptr<TimeProofService> _timeProofService;
+
+    // the mutex protects _clusterTime
+    stdx::mutex _mutex;
+    SignedLogicalTime _clusterTime;
+    const bool _validateProof;
+};
+
+}  // namespace mongo